Synthesis and characterization of polyurethane-grafted single-walled carbon nanotubes via click chemistry

Polyurethane (PU)-grafted carbon nanotubes were synthesized by the coupling of alkyne moiety decorated single walled carbon nanotube (SWCNT) with azide moiety containing PU using Cu(I) catalyzed Huisgen [3 + 2] cycloaddition click chemistry. The azide moiety containing poly(s-caprolactone)diol was synthesized by ring-opening polymerization and further used for PU synthesis. Alkyne-functionalizion of SWCNT was completed by the reaction of p-aminophenyl propargyl ether with SWCNT using a solvent free diazotization procedure. Nuclear magnetic resonance, Fourier transform infrared, and Raman spectroscopic measurements confirmed the functionalization of SWCNT. Scanning electron microscopy and transmission electron microscopy images showed an excellent dispersion of SWCNTs, and specially debundling of SWCNTs could be observed due to polymer assisted dispersion. A quantitative grafting was successfully achieved even at high content of functional groups.     

Photoactive multi-walled carbon nanotubes: synthesis and utilization of benzoin functional MWCNTs

This study describes a facile method for the synthesis of functionalized multi-walled carbon nanotubes (MWCNTs) carrying photoactive group. The synthesis of MWCNTs-based macro-photoinitiator was achieved by the esterification reaction between benzoin moiety and acyl chloride functional MWCNTs. Synthesized MWCNT-based photoinitiator (MWCNTs–benzoin) was used in the photopolymerization of styrene to yield polystyrene (PS)-grafted MWCNTs (MWCNTs–PS) by “grafting from” method. The efficiency of MWCNTs–benzoin photoinitiator was determined by evaluating the effect of initiator to monomer ratio and reaction period on photopolymerization of styrene. Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy analyses confirmed the covalent bonding for functionalization of MWCNTs and determined the final structures. Thermogravimetric analysis, gel permeation chromatography and UV spectroscopy were performed to evaluate the grafting efficiency of PS that covalently grafted to MWCNTs, and high efficiency of MWCNTs–benzoin as a macro-photoinitiator was also confirmed. Scanning electron microscopy was used to determine the surface morphology of functionalized MWCNTs and MWCNTs–PS.     

Fumed silica/polymer hybrid nanoparticles prepared by redox-initiated graft polymerization in emulsions

Hybrid particles comprising aggregated fumed silica nanoparticles as the core and hydrophobic polymers existing around the nanoparticles were prepared by ‘grafting from’ polymerization in emulsions. The emulsion polymerization employed cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and sodium dodecyl sulfate (SDS) as an anionic surfactant, respectively, to stabilize the emulsion polymerization. The polymerization was initiated by the redox reaction between ceric ion Ce(IV) and the amine groups on the surfaces of aminated fumed silica nanoparticles that were modified by 3-aminopropyltriethoxysilane. Infrared spectroscopy and thermogravimetric analysis demonstrated that both poly(methyl methacrylate) (PMMA) and polystyrene (PS) were successfully grafted onto the fumed silica surface. The type of surfactant greatly affected the grafting ratio, monomer-to-polymer conversion, and morphology of the product. When CTAB was used as the surfactant, both the grafting ratio and monomer-to-polymer conversion were lower than when SDS was used, but transmission electron microscopy and light scattering analysis indicated that most of the resultant particles were sub-100 nm hybrid nanoparticles with a non-spherical shape and particles sizes of 75–90 and 57–85 nm for PMMA and PS-grafted fumed silica, respectively. Whereas, when SDS was used as the surfactant, the particles agglomerated to form large irregular clusters or even networks, possibly due to the electrostatic attractions between SDS and Ce(IV) and/or the aminated fumed silica nanoparticles in aqueous solution.     

Preparation and decoloration property of polystyrene-grafted palygorskite nanoparticles

The polymerization of styrene on inorganic palygorskite nanorods was carried out by reverse atom transfer radical polymerization (RATRP) in a completely controlled manner to form structurally well-defined PS-grafted hybrid nanocomposite. Well-defined PS chains were grown from the nanoparticle surfaces to yield individual particles composed of a palygorskite core and a well-defined outer PS layer. It has been found that the dispersibility of palygorskite particles in organic solvents is significantly improved by grafting polymers onto the surface of palygorskite particles. So the holding time of PS-palygorskite is prolonged in organic solvents. Active point of adsorption in palygorskite surface is adequately utilized. The polymer-grafted palygorskite nanoparticles possess excellent decoloration capacity in organic solvents.     

Preparation of covalently functionalized graphene using residual oxygen-containing functional groups

When fabricated by thermal exfoliation, graphene can be covalently functionalized more easily by applying a direct ring-opening reaction between the residual epoxide functional groups on the graphene and the amine-bearing molecules. Investigation by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) all confirm that these molecules were covalently grafted to the surface of graphene. The resulting dispersion in an organic solvent demonstrated a long-term homogeneous stability of the products. Furthermore, comparison with traditional free radical functionalization shows the extent of the defects characterized by TEM and Raman spectroscopy and reveals that direct functionalization enables graphene to be covalently functionalized on the surface without causing any further damage to the surface structure. Thermogravmetric analysis (TGA) shows that the nondestroyed graphene structure provides greater thermal stability not only for the grafted molecules but also, more importantly, for the graphene itself, compared to the free-radical grafting method.     

Concise route to styryl-modified multi-walled carbon nanotubes for polystyrene matrix and enhanced mechanical properties and thermal stability of composite

Effective functionalization of multi-walled carbon nanotubes (MWCNTs) with styryl group was carried out via the esterification reaction of the carboxylate salt of carbon nanotubes and 4-vinylbenzyl chlorides in toluene. The functionalized MWCNTs were characterized through FTIR and Raman spectra to confirm the styryl groups covalently connected to the surface of MWCNTs. The weight loss of functionalized moieties determined by thermogravimetry-differential scanning calorimertry analysis is around 36%. Nanotube-reinforced polystyrene were fabricated by mixing functionalized MWCNTs and polystyrene. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the functionalized nanotubes had a better dispersion than the unfunctionalized MWCNTs in the matrix. Moreover, styryl-modified MWCNTs/PS nanocompsite presented obvious improvements in mechanical properties and thermal stability.     

The influence of carbon nanotube functionalization route on the efficiency of dispersion in polypropylene by twin-screw extrusion

The joint effect of chemical functionalization and polymer melt blending conditions on carbon nanotube dispersion in polypropylene, as well as its influence on the electrical and mechanical properties of the resulting composites were investigated. Melt blending was performed using a prototype twin screw extruder enabling sampling along the barrel. The carbon nanotube dispersion was assessed by optical and scanning electron microscopy. The functionalization reaction was tailored for compatibility with the polymer, and characterized by X-ray photoelectron spectroscopy. In particular, nanotubes covalently bonded to polypropylene showed distinctive dispersion ability, while the carbon nanotube dispersion remained stable even after re-melting. However, the polypropylene-functionalized nanotubes produced composites with higher electrical resistivity, possibly due to the insulating effect of the polymer bonded to the nanotubes surface.     

利用原子转移自由基反应在超大孔聚苯乙烯微球表面接枝含糖聚合物刷

超大孔聚苯乙烯微球具有力学强度高、化学稳定性好、传质速率快等优点,但其表面疏水性强,无法衍生,要想用作生物大分子分离介质必须对其亲水改性。文中利用原子转移自由基(ATRP)反应的方法在超大孔聚苯乙烯微球(PS)表面原位接枝含糖聚合物刷,得到亲水改性的超大孔聚苯乙烯微球。对溶剂、配体、催化剂及温度等反应条件进行了详细考察,优化了接枝反应条件。含糖聚合物刷最大接枝量达到490.8 mg/g干球,改性后微球表面接触角由124°下降到42°,对蛋白的吸附量也降低了10.2倍,亲水性和生物相容性明显提高,同时微球的超大孔未被堵塞,且柔性含糖聚合物刷在后期衍生过程中还起到了"间隔臂"的作用,将是一种非常优良的生物大分子分离介质,在快流速蛋白分离色谱领域有很大应用潜力。     

Functionalization of nitrogen-doped carbon nanotubes with gallium to form Ga-CN(x)-multi-wall carbon nanotube hybrid materials

In an effort to combine group III-V semiconductors with carbon nanotubes, a simple solution-based technique for gallium functionalization of nitrogen-doped multi-wall carbon nanotubes has been developed. With an aqueous solution of a gallium salt (GaI(3)), it was possible to form covalent bonds between the Ga(3+) ion and the nitrogen atoms of the doped carbon nanotubes to form a gallium nitride-carbon nanotube hybrid at room temperature. This functionalization was evaluated by x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy.     

"Hairy" single-walled carbon nanotubes prepared by atom transfer radical polymerization

"Hairy nano-objects" are hybrid nanostructures comprising a core surrounded by a "hairlike" corona of flexible polymer chains, the role of which is typically to improve the solubility of the core material or to improve its dispersability and adhesion in other polymer matrices. Both aspects could be particularly useful with carbon nanotubes, especially in their applications as reinforcing agents. The controlled synthesis of hairy carbon nanotubes is accomplished by chemical modification with 2-bromopropionate followed by extension with poly(n-butyl acrylate) through atom transfer radical polymerization. The obtained hairy nanotubes are visualized at nearly molecular resolution with tapping-mode atomic force microscopy, providing insight into the uniformity of grafted chain lengths and grafting density. The grafting densities vary from approximately 1.0-10.0 chains nm(-1) along the nanotubes. Such a wide range of grafting density may indicate some chemical heterogeneity along and between the nanotubes; it may be also an indication of the challenges associated with carrying out chemical modification of nano-objects having high tendency to aggregate.     

Preparation and characterization of poly(N-isopropylacrylamide) films on a modified glass surface via surface initiated redox polymerization

A functionalization with 3-aminopropyltriethoxysilane (APTES) monolayer of a hydroxylated glass surface, followed by the surface initiated graft radical polymerization of N-isopropylacrylamide (NIPAm) using amino groups of APTES monolayer chemical bonded with glass surface and Ce⁴⁺ as a redox initiating system. The microstructure of poly(N-isopropylacrylamide) (PNIPAm) film obtained from the redox graft polymerization on the modified glass surfaces was examined by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), and the results showed that about 60 nm thickness of thermosensitive polymer (PNIPAm) film successfully formed.     

Functionalization of multi-walled carbon nanotubes with bis(2,2':6',2"-terpyridine) ruthenium(II)-connected diblock polymer

Multi-walled carbon nanotubes (MWCNTs) were functionalized with a bis(2,2':6',2"-terpyridine) ruthenium(ll)-connected diblock poly(N-isopropyacryamide) (RuTpyPNIPAM) by a simple methodology of covalent amidation. The composition and structure of the functionalized ruthenium multi-walled carbon nanotubes (RuMWCNTs) were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and scanning electron microscopy (SEM). These characterization methods confirm that after functionalization, ruthenium metallopolymer are interconnected or attached as aggregated structures on the surface of the carbon nanotubes.     

Controlled fabrication of theophylline imprinted polymers on multiwalled carbon nanotubes via atom transfer radical polymerization

Theophylline imprinted polymers were synthesized on the surface of multiwalled carbon nanotubes via atom transfer radical polymerization using brominated multiwalled carbon nanotubes as an initiator. The nanotube-based initiator was prepared by directly reacting acyl chloride-modified multiwalled carbon nanotubes with 2-hydroxylethyl-2'-bromoisobutyrate. The grafting copolymerization of 2-hydroxyethyl-2-methyl-2-propenoate and ethylene glycol dimethacrylate in the presence of template theophylline led to thin molecularly imprinted polymer films coating multiwalled carbon nanotubes. The thickness of molecularly imprinted polymer films prepared in this study was about 5 nm as determined by transmission electron microscopy. Fourier-transform infrared spectroscopy was utilized to follow the introduction of initiator groups as well as polymers on the carbon nanotube surfaces. Thermogravimetric analysis indicated that the molecularly imprinted polymers were successfully grown from the carbon nanotube surfaces, with the final products having a polymer weight percentage of ca. 50 wt%. The adsorption properties, such as adsorption dynamics, special binding and selective recognition capacity, of the as-prepared molecularly imprinted polymer films were evaluated. The results demonstrated that the composite of molecularly imprinted polymers and multiwalled carbon nanotubes not only possessed a rapid dynamics but also exhibited a good selectivity toward theophylline, compared to caffeine.     

PP/碳纳米管复合材料的制备及电性能

采用原子转移自由基(ATRP)活性聚合方法在多壁碳纳米管(MWNT)表面接枝丙烯酸丁酯聚合物(PBA),并以此对聚丙烯(PP)进行改性。红外光谱(FT-IR)及透射电子显微镜(TEM)测试结果表明,采用ATRP法成功地将PBA接枝到多壁碳纳米管(MWNT)表面。对PP/MWNT复合材料电性能研究表明,MWNT-PBA的添加比MWNT-COOH更能降低复合材料的电阻率。MWNT-PBA的加入可使PP从绝缘材料转变为抗静电材料。MWNT-PBA和MWNT-COOH加入PP都能提高材料的电性能,而MWNT-PBA比MWNT-COOH的作用更加明显。     

In situ polymerized nanocomposites: Polystyrene/CNT and Poly(methyl methacrylate)/CNT composites

Carbon nanotubes (CNTs) were incorporated into polystyrene (PS) and poly(methyl methacrylate) (PMMA) matrices via in situ emulsion and emulsion/suspension polymerization methods. The polymerizations were carried out using various initiators, surfactants, and carbon nanotubes to determine their influence on polymerization and on the properties of the composites. The loading of CNTs in the composites varied from 0 to 15 wt.%, depending on the CNTs used. Morphology and dispersion of the CNTs were analyzed by transmission and scanning electron microscopy techniques. The dispersion of multi-walled carbon nanotubes (MWCNT) in the composites was excellent, even at high CNT loading. The mechanical properties, and electrical and thermal conductivities, of the composites were also analyzed. Both electrical and thermal conductivities were improved.     

Dispersion of single-walled carbon nanotubes in aqueous and organic solvents through a polymer wrapping functionalization

The processing and application of single-walled carbon nanotubes (SWNTs) is limited by their purity and dispersion in most common solvents. Non-covalent polymer wrapping functionalization of SWNTs provides an excellent route to improve their property and thus the dispersion in aqueous and organic solvents occurred simultaneously. This paper reports the purification and a methodology for obtaining dispersion of SWNTs, obtained by arc-discharge, using a biocompatible water soluble polymer which, presumably, wraps around nanotubes. Scanning electron microscope (SEM) and high resolution transmission electron microscope (HR-TEM) were employed to examine the dispersion. UV-Vis-NIR spectroscopy further substantiates the presence of dispersed SWNTs in aqueous solution. Raman spectroscopy reveals the impact of chemical and ultrasonic processing on the structural order of the nanotubes. No trace for structural damage has been observed from the Raman studies and so, our treatment is considered as a physical rather chemical process. The polymer treated tubes become more hydrophilic which was confirmed by contact angle measurement.     

In-situ synthesis of polymer – silica nanocomposites by living radical polymerisation using TEMPO initiator

In situ synthesis of polystyrene nanocomposites by living free radical polymerisation using intercalated TEMPO (2,2,6,6 tetramethyl piuperidine-N-oxy)-mediated chain transfer agent in the layers of montmorillonite clay is reported. An ammonium initiator to be used for nitroxide-mediated radical polymerisation (NMRP) was synthesised in a three-step procedure. The esterification of 11-bromo-1-undecanol with α-phenyl chloroacetyl chloride yielded α-phenyl chloroacetylated undecanol. Second, the chlorine groups were converted to nitroxide-mediated groups by coupling with 1-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO–OH). The subsequent reaction of NMRP macroinitiator with trimethylamine produced the NMRP surface modifier. These modified clays were then dispersed in styrene (St) monomers in different loading degrees to carry out the in situ free radical polymerisation. The intercalation ability of the chain transfer agent and exfoliated nanocomposite structure were evidenced by both X-ray diffraction (XRD) spectroscopy and transmission electron microscopy. Thermal properties and morphologies of the resultant nanocomposites were also studied.     

悬浮聚合法制备聚苯乙烯磁性微球

本文以聚乙烯醇/水为介质,苯乙烯为单体,在经3-甲基丙烯酰氧基丙基三甲氧基硅烷(3-MPS)表面修饰的Fe3O4磁性颗粒的存在下,采用悬浮聚合法,制备了聚苯乙烯磁性微球。分别用X-射线衍射(XRD)、原子力显微镜(AFM)、热重分析(TGA)、傅里叶变换红外光谱仪(FTIR)、振动样品磁力计(VSM)等方法对磁性微球的结构和性能进行了表征。实验结果表明,所合成的磁性微球为球型结构,平均粒径约为2μm,尺寸分布较均匀,具有超顺磁性。     

两亲性嵌段共聚物改性的多壁碳纳米管的制备

通过对碳纳米管进行表面改性制得具有引发ATRP反应活性的碳纳米管(MWNT-Br),以MWNT-Br作引发剂经过两次ATRP反应将聚乙烯基吡咯烷酮(PVP)和聚甲基丙烯酸特丁酯(PtBMA)先后接枝到多壁碳纳米管表面制得两亲性嵌段共聚物接枝的碳纳米管(MWNT-PVP-b-PtBMA),用红外光谱、热失重和透射电镜对两亲性碳纳米管进行了表征.并考察了修饰前弱亲油性的纯碳纳米管、酸化后亲水性的碳纳米管和修饰后两亲性碳纳米管这3种碳纳米管在水和氯仿形成的两相体系中的分散情况,观察到所制备的两亲性碳纳米管能够均匀分散在油水两相界面上.     

Preparation polystyrene/multiwalled carbon nanotubes nanocomposites by copolymerization of styrene and styryl-functionalized multiwalled carbon nanotubes

Styryl-functionalized multiwalled carbon nanotubes (p-MWNTs) were prepared by esterification based on the carboxylate salt of carbon nanotubes and p-chloromethylstyrene in toluene. Then in situ radical copolymerization of p-MWNTs and styrene initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was applied to synthesize composites of styryl-functionalized multiwalled carbon nanotubes and polystyrene (PS) (p-MWNTs/PS). Characterizations carried out by FT-IR, ¹H NMR, UV–vis show that styryl group covalently bond to the surface of MWNTs. The results of UV showed that the solutions of p-MWNTs/PS in chloroform have the hyperchromic effect. Transmission electron microscopy (TEM) images of p-MWNTs/PS composites and scanning electron microscopy (SEM) images of fracture surface of p-MWNTs/PS composites showed the functionalized nanotubes had a better dispersion than that of the unfunctionalized MWNTs in the matrix. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) suggested that the thermal stability of p-MWNTs/PS composites improved in the presence of MWNTs.